Amplifier circuits



Patented Feb. 5, 1935 assign'or to- Radio Gorporation' of corporation of Delaware America, a

Applicationoctober 28, 1931, Serial No. 571,491 V In Gc'r'm any April 18;" 1931" '11 Glaifnsz' (01. 179- 171) The invention relates-toe; device for automatically controlling the output energy of amplifiers.

An automatic volume control: can be obtained by" altering the grid bias of one, or more, of: the

thermionicv tubesutilized, or, again, by'bridging' one, or more; circuits: of the-arrangement by an impedance which is variablein accordance :with:

" impedance, and, therefore; a decrease of the pcthe intensity of the signals: received.

According. to theinventiomnuse is made of the energy to be amplified.

The novel features which I believe to be characteristic of myinvention are set forth inparticularity in the appended claims, the invention itself, however, as-to both its-organization and method of operation will-best be understood by-referenceto the followingdescription-taken in-connection;

0 with the drawing: in whichl have indicated diagrammatically" several circuit arrangements for carrying Lmy invention; into effect.-

The invention will be explained more reference to the drawing which represents,= by way of example some embodimentsthereon Fig. 1 represents a circuit arrangement; in

which the 'en'ergy'to be amplified is suppliedat the points land 2-.-- Thepointlis connected, through sure that both the positive andthe negative portions of the potentials tobe amplified areim fiuenced in thesame manner, the tubes 5 and 6 are oppositely connected.

That -is--to say: the anode-of-the tube 5' is con nected to the middle of the cathode of the tube 6, and the middle of the cathode of the tube 5 is connected to the anode of the tube 6. The output circuit of the tube 4 comprises the primary winding 7 of a transformer with three secondary windings 8, 9 and 10. The winding 8 supplies the amplified energy to the input circuit of a following amplifying tube, or to a sound reproducing device, whereas the windings 9 and 10 serve to feed the cathodes of the tubes 5 and 6. The device operates as follows: If a determined potential is applied to the points 1 and 2 of the circuit arrangement, this potential will be amplified by the tube 4. The current in the output impedance sets up in the windings 9 and 10 a potential which feeds the cathodes of the tubes 5 and 6. Thus, the feeding of the tubes 5 and 6 is dependent on the current in the output imlatter measure, and. for the: variable impedance are utilized one, or more, thermionic tubjes whose cathodes are heated in dependency fromthe pedance and, thereforeon the energy to be amplified.- The internal resistance of the thermionic tubes variesdue to the variation of the heating voltage. A second impedance of' variable value is consequently connected in parallel to the input impedance of the tube 4. An increase of the-output energycauses a decrease of' said variable tential on the input electrodes of the amplifying tube. 10

1 The most favorable operation-is obtained when the internal resistance of the tubes 5 and 6 is of the order of magnitude ofthe further impedance in the input circuit. Since this input impedance is asa rule small relative to the internal resistance 15 ofthe tubes5 and'6,.there is provided a series resistance 3 which may be adjustable in order to obtain an exact adaptation. Besides, said resistance 3 allows of influencing the intensity of the" controlling effect of the device. 20

It is evident that various sm'allmodifications may be made in theicircuit arrangement above described, while notwithstanding the desired effeet is obtained; Thus, for example; theva'riable impedance may beconnected into anyidesired iiiputor output circuit of a multi-stage amplifier. When this impedanceis included in a circuit in which exclusively flows a pulsatory'diiect current, one ofthe tubes 5 and6 connected in parallel butcontrarily-. will be suflicient; If'the tub'es 5.- and 6 are indirectly heated," asingle winding may besubstitutedlfor the transformer windings il -and 10. U

If'f'or the amplifying tub'es resistance coupling instead or transformer coupling" is utilized; use may be made of the circuit arangemerit representedin Fig. 2'; This circuit arrangement is substantially similarto that shown'in Fig; 1, the only difference is that the output transformer is replaced by an ohmic resistance a portion of which is branched for the feeding of the filaments of the tubes 5 and 6 which are represented in this figure as indirectly heated tubes. Besides, it may be advisable to provide the heating current conductors of the tubes 5 and 6 with adjustable re- 45 sistances in order to obtain the most favorable adjustment of the internal resistance of these tubes. These resistances may also serve to influence the controlling effect. It has been found that the method above described permits obtaining a very satisfactory control of the output energy of an amplifier.

While I have indicated and described several systems for carrying my invention into effect, it will be apparent to one skilled in the art that my invention is by no means limited to the particular organizations shown and described, but that many modifications may be made without departing from the scope of my invention as set forth in the appended claims.

What is claimed is:

1. An amplifier comprising an electron discharge tube provided with an input and output circuit, a variable impedance path connected in shunt across the input impedance of said amplifier tube input circuit and including a space discharge device, provided with at least a cathode and anode, and means between the said output circuit and said path for controlling the electron emissivity of said device in accordance with the fiow of current in said output circuit whereby the total input impedance of said amplifier is adjusted.

2. An automatic volume control arrangement for an amplifier provided with an input circuit and an output circuit, said arrangement comprising a diode having its anode connected to the grid of said amplifier tube, and its filament connected to the cathode of said amplifier tube, and means for coupling the filament of the diode solely to the amplifier anode circuit whereby the diode filament is energized in accordance with variations in the amplifier anode circuit current.

3. An automatic volume control arrangement for an amplifier provided with an input circuit and an output circuit, said arrangement comprising a diode having its anode connected to the grid of said amplifier tube, and its cathode connected to the cathode of said amplifier tube, and means for coupling the cathode of the diode to the amplifier output circuit in such a manner that the diode cathode is energized in accordance with variations in the amplifier output circuit current and a second diode having its cathode connected to said amplifier'grid and its anode connected to said amplifier cathode, and means for coupling the second diode cathode to the amplifier output circuit in a manner similar to the coupling to said first diode cathode.

4. An automatic volume control arrangement for an amplifier provided with an input circuit and an output circuit, said arrangement comprising a diode having its anode connected to the grid of said amplifier tube, and its cathode connected to the cathode of said amplifier tube,

means for coupling the cathode of the diode solely to the anode circuit of said amplifier tube whereby the diode cathode is energized in accordance with variations in the amplifier anode circuit current, and a variable resistor connected in the grid side of said amplifier input circuit.

5. An amplifier circuit arrangement comprising a device for controlling the output energy, a variable impedance, comprising two tubes connected in parallel but contrarily, bridged across the amplifier input circuit, and means for heating the filaments of said two tubes in accordance with the intensity of amplified energy.

6. An amplifier circuit arrangement comprising a device for controlling the output energy, a variable impedance, comprising twotubes connected in parallel but contrarily, bridged across the amplifier input circuit, and means including a variable resistor in the amplifier anode circuit for heating the filaments of said two tubes in accordance with the'intensity of amplified en- '7. An amplifier circuit arrangement comprising a device for controlling the output energy, a variable impedance, comprising two tubes of the indirectly heated cathode type connected in parallel but contrarily, bridged across the amplifier input circuit, and means for heating the heater filaments of said two tubes in accordance with the intensity of amplified energy.

8. In combination with an amplifier having an input circuit and an output circuit, said input circuit being adapted for connection to a source of signal energy, an impedance path connected between the grid and cathode of the amplifier in parallel with the input impedance of said amplifier, said path including at least one tube provided with at least an anode and a cathode, and a connection between said tube and the amplifier output circuit for varying the emissivity of the cathode of said tube in accordance with the variation in intensity of the signal current flow in the said output circuit, the relative values of the impedances of said path and said input impedance being so chosen that emissivityvariation resultsin an automatic variation of the signal energy impressed upon said input circuit.

9. In an arrangement as in claim 8, a variable resistor in the said input circuit for adjusting said relative values. 7

10. In an arrangement as in claim 8, said connection being disposed between the cathode of said tube and the anode circuit of the amplifier, and a second tube connected in parallel with the first tube, the secondtube cathode being energized from said amplifier anode circuit.

11. An arrangement as in claim 8, wherein said tube comprises a diode whose anode is connected to the amplifier grid and whose cathode is connected to the amplifier cathode, and said relative values being such that the path impedance is of the same order of magnitude as said amplifier input impedance.

ANTON LEENDERT TIMMER. 

